Calorimetry is a universal analytical method that measures heat or heat release rate from a biological, chemical or physical sample or process. There are three main categories of calorimeters: temperature scanning calorimeters, isothermal and adiabatic. Differential scanning calorimeter is the most popular temperature scanning calorimeter in which the difference in the form of heat or temperature between the sample and reference is measured as a function of scanned temperature. Differential scanning calorimeters or DSCs use a “dual-cell” design, commonly referred to as a “differential-channel” or “reference-channel” design. This type of “dual-cell” calorimetric design, which consists of a sample channel and a reference channel, is fundamentally different from single channel design in both control and functionality. DSCs have been used widely to study thermophysical or thermochemical properties of materials with a typical sample size in the range of milligrams. Conversely, due to lack of sensitivity, the single-channel scanning calorimeter, i.e., the device without a reference channel, is not popular and mostly used for rough screening purpose. One of the major disadvantages of temperature scanning calorimetry is that the time-resolved thermochemical information cannot be experimentally obtained.
Isothermal calorimeters are used mainly for monitoring time-resolved reaction processes, because many of the desired manufacturing processes in the chemical and pharmaceutical industry are isothermal. While liter-scale reactions are normally tested on single channel isothermal reaction calorimeters, gram-scale reaction calorimetric studies are typically performed on isothermal microcalorimeters (e.g., SuperCRC™ isothermal reaction microcalorimeter) using the differential or referencing calorimetric design principle similar to that of DSCs.
Adiabatic calorimetry has been also used for physical property measurement (e.g., specific heat and phase transfer studies) and reaction process monitoring (e.g., chemical reaction upon mixing or decomposition upon temperature rise). More recently, adiabatic calorimeters have been used to measure temperature and pressure as a function of time in order to look at undesired chemical reactions. When chemical mixing, reaction or decomposition becomes exothermic, the heat released from the sample may cause a significant temperature excursion, and sometimes develop into a self-perpetuated, thermal runaway reaction. Current adiabatic calorimeters are all single channel devices.
To study this self-perpetuating reaction, an adiabatic calorimeter, called the accelerating rate calorimeter (ARC), was developed (U.S. Pat. No. 4,208,907). However, this single-channel calorimeter is a quasi-adiabatic device, since a large portion of the heat released by sample is absorbed by or sinks to the sample container. Because this heat sink effect, the experimental temperature rise and the rate of temperature rise are, therefore, dampened or lower than the theoretical limits, causing a so-called “thermal lag” effect that significantly slows down the reaction progress and results in an erroneous time to maximum rate (TMR), a critical value in runaway reaction hazard assessment. Another single-channel adiabatic calorimeter with a compensation approach was also developed (U.S. Pat. No. 4,130,016), with the idea that the heat-sink heat loss could be compensated by using a compensation heater which is attached to the outer wall of the sample container. However not only did the device fail to deliver a calorimetric result better than 95%, it also is difficult to downsize this liter-scale container to meet the analytical lab standards, and therefore has never been commercialized.
Since the early 2000s, some single-channel scanning calorimeter devices were developed in order to reduce the container heat-sink effect and reach a higher adiabaticity (U.S. Pat. No. 6,157,009 and U.S. Pat. No. 7,021,820). However, these scanning devices are neither adiabatic nor isothermal, therefore, the time-resolved temperature and pressure information, such as the maximum adiabatic temperature rise and time to maximum rate (TMR), can't be measured on these devices.
Although the differential compensation principle has been used in the instrument design of several commercial isothermal and DSC calorimeters, it has never been used in adiabatic calorimetry. In contrast to prior quasi-adiabatic calorimeters, the present invention is a differential compensation adiabatic calorimeter, which is a unique instrument in the field of calorimetry. In this true adiabatic mixing and reaction calorimeter, the sample heat-sink heat loss to the sample container can be fully compensated so that the reaction can be conducted in a truly adiabatic state. The differential adiabatic compensation feedback circuit guaranties that neither under-nor over-compensation is made, 100% adiabaticity is achieved, the maximum temperature rise, time to peak temperature and time to maximum rate all can be experimentally measured without thermal lag.